Vertical crossover elimination



Feb. z3, 1943. A. G. KANESOIAN 2,311,837

VERTICAL CROSSOVER ELIMINATION Filed July 26, 1941 1 l zfAn/TENNA Le MEAN-5 J5 1.--.! J0, j?

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Z0 THA/VM/f@ PHASE CUN-NZD" MEANS INVENTOR BY al Patented Feb. 23, 1943 UNETED STATES VERTICAL CROSSOVER ELIMINATION Armig G. Kandoian, New York, N. Y., assignor to Federal Telephone & Radio Corporation, a corporation of Delaware Application July 26, 1941, Serial No. 404,147 a claims. gol. 25o-11) My invention relates to improvements in antenna directive systems, and more particularly to improvements in course beacon arrays of the nature disclosed in my copending application Ser. No. 316,728, filed February 1, 1940.

It is an object of the invention to eliminate sources of error and false courses in beacon arrays of the above mentioned type.

It is a more specific object to eliminate crossover patterns in the vertical plane, whereby certain false course indications may be avoided.

Other objects and various further features of novelty and invention will hereinafter be pointed out or will become apparent from a reading of the following specification in conjunction with the drawing included herewith. In said drawing:

Fig. 1 is a schematic plan-view showing of a four course beacon antenna array;

Figs. 2, 3, and l are diagrams illustrative of radiation patterns of the array of Fig. 1 in the horizontal and vertical planes; and

Fig. 5 is a schematic showing of antenna feeding means in accordance with the invention.

Directive antenna arrays, such as those disclosed in the above-mentioned application, have been proposed in order to provide a rather large plurality of course indications and at the same time to eifect an economy of antenna apparatus. In the case referred to it was shown, for example, how four courses, defined by Crossovers in the horizontal plane, could be set up by a ve element antenna array. A plan view of such an array is shown schematically in Fig. 1.

The array of Fig. 1, as explained by the said application, preferably includes five similar nondirective antenna elements 5, 6, l, 8, and 9. The first four of these elements are disposed generally at the corners of a square and element 9 is located generally centrally thereof. In accordance with the prior disclosure at any given time a set of three diagonally aligned elements, say 5-9-6 (shown by circles) or '1 9-8 (shown by squares) is fed at any one instant, and in a preferred form keying means (not shown in Fig. 1) are provided for keying one set with A identification signals and the other with N signals. When energy of this nature is thus supplied to the array and a spacing of between 1/2 to 7/2 or 53; of the carrier wavelength is employed between element 9 and any of the outer elements, the familiar radiation pattern of Fig. 2 will result in the horizontal plane. In this gure, one signal, say the N characterized one. may set up a pattern Ill; and the other or A signal, resulting from keying elements 5, 9, and 6 may set up a similar pattern Il. In a known manner the overlapping portions of the lobes of patterns l0 and Il serve to identifyfour courses I2, I3, I4, and l5, as will be clear.

Desirable as the above arrangement may seem for establishingffour courses, I have found that certain serious errors in course readings obtained on aircraft occur when the vertical angle of the airplane to the arraybecomes at all steep, say above 30. I have found that these false `indications can be caused by parasitic reflection due to the non-energized elements and occurring When one set of elements is energized. A graphic illustration of the effect of such parasitic reflection is shown in Fig. 3 which is a vertical sectional view in space, taken through the array. In this figure the directly propagated Wave pattern due to the propagating set of elements, say 5, 9, 6, takes the form of a pair of large outwardly sweeping lobes I6, Il. At the instant of such transmission elements 'I and 8 are not energized, but these elements act as reflectors and have been found to cause minor lobes I8, I9.

At relatively high elevational angles it is clear from Fig. 3 that, inasmuch as the minor lobes I8, I9 are more vertically inclined than major lobes I6, Il, these minor lobes represent radiation of a magnitude predominating over that of the major lobes. The horizontal plane radiation pattern of energy reected by elements 'I and 8 and forming the minor lobes is necessarily considerably at variance with that needed to form the desired courses of Fig. 2. As a result false signals and radiation patterns are transmitted at such greater elevations, and false courses are obtained. The elevation angle of the Crossovers or critical vertical elevation angles above which this error occurs is naturally determined by the angle at which major lobe radiation (direct propagation) equals minor lobe radiation (parasitic reiiection), as will be clear.

To. eliminate the above-indicated source of error and obtain the clear pattern I6', l1' of Fig. 4, it is clearly necessary to render negligible or absolutely eliminate the minor lobes. I have found that such elimination may be accomplished by appropriately detuning the effective lengths of the non-energized outer antenna loops or elements while the other loops are being fed. Such complete detuning may be accomplished by providing appropriate phase control means in the supply lines for both sets of outer elements or by designing these portions of the circuit inherently to be detuned at the operating frequency.

A preferred arrangement of my proposed system is shown schematically in Fig. 5. In. this layout a transmitter 20 continuously supplies carrier energy to the center antenna element 9. Key means 2l serves alternatively to feed this carrier energy to the two sets of outer elements 5, 6 and 1, 8 in accordance With A and N or other characterizing rhythm. As above-indicated, each line supplying a set of outer elements may be provided With adjustable phase-control means 22, 23 rendering one of the supply lines completely detuned when it is not energized; thus, When elements E, 6 are energized, the effective length of the open line from key 2| to and including elements l, 8 is such as to form a` non-resonant circuit, and the converse is true. for elements 5, 6 when loops 1, 8 are energized.'

If desired, phase control means 24 may be provided in the supply line to the central antenna 9 for appropriate tuning adjustment at the operating frequency. v

While I have shown and described my invention in particular detail in connection with the preferred form shown, it is to be understood that various modifications, additions and omissions may be made fully Within the scope thereof.

What is claimed is:

1. A multi-course beacon antenna array system comprising a first antenna element, four other antenna elements each substantially equally spaced from said rst antenna .element and from each other, supply-line means for each of said antenna elements, a source of radio frequency energy, keying means alternately connecting said radio frequency energy to one pair of opposed antenna elements of said four and to another pair of opposed elements of said four, means supplying said radio frequency energy to said first antenna element, and phase-control means included in said supply-line means, said phasecontrol means being adjusted to detune said supply-line means and said pairs of antenna elements during the period rthey are disconnected from said source.

2. A multi-course beacon antenna array system comprising a first antenna element, four other antenna elements each substantially equally spaced from said rst antenna element and from each other, transmission line means connecting one pair of opposed antenna elements of said four, further transmission line means connecting another pair of opposed elements of said four, a source of radio frequency energy, the effective length of each of said transmission line means and said respective pairs of antenna elements being such as to detune said line means and said elements at said radio frequency energy, keying means alternately connecting said source of radio frequency energy to said pairs of antenna elements, and a connection from said source of radio frequency energy to said rst antenna element.

3. A multi-course beacon antenna array system comprising a first antenna element disposed generally centrally of four generally parallelogram-spaced antenna elements, means for alternately supplying pairs of opposed elements of said four with radio frequency energy, means for supplying said rst element with radio frequency energy, and means for detuning each of said pairs of opposed `elements during the time no energy is being supplied thereto.

ARMIG G. KANDOIAN. 

